Honeycomb filter

ABSTRACT

A honeycomb filter includes a pillar-shaped honeycomb structure body having a porous partition wall disposed to surround a plurality of cells and a plugging portion, wherein the partition wall is composed of a material containing cordierite as a main component thereof, porosity of the partition wall measured by a mercury press-in method is 60 to 68%, an average pore diameter of the partition wall measured by a mercury press-in method is 13 to 18 μm, and in a pore diameter distribution indicating a cumulative pore volume of the partition wall measured by a mercury press-in method, with a pore diameter (μm) on an abscissa axis and a log differential pore volume (cm3/g) on an ordinate axis, a first peak including a maximum value of the log differential pore volume has a pore diameter value of 15 μm or less, the pore diameter value corresponding to a ⅓ value width of the maximum value.

The present application is an application based on JP 2020-034888 filedon Mar. 2, 2020 with Japan Patent Office, the entire contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a honeycomb filter. More specifically,the present invention relates to a honeycomb filter which has hightrapping performance and reduces pressure loss, and further exhibitshigh purification performance by being loaded with an exhaust gaspurifying catalyst.

Description of the Related Art

Hitherto, as a filter adapted to trap particulate matter in exhaust gasemitted from an internal combustion engine, such as an automobileengine, or a device adapted to purify toxic gas components, such as CO,HC, and NOx, there has been known a honeycomb filter using a honeycombstructure (refer to Patent Documents 1 and 2). The honeycomb structurehas a partition wall formed of porous ceramic, such as cordierite, andincludes a plurality of cells defined by the partition wall. In thehoneycomb filter, the foregoing honeycomb structure is provided withplugging portions that alternately plug the open ends on the inflow endface side and the open ends on the outflow end face side of theplurality of cells. In other words, the honeycomb filter has a structurein which inflow cells having the inflow end face side open and theoutflow end face side plugged and outflow cells having the inflow endface side plugged and the outflow end face side open are arrangedalternately with the partition wall therebetween. Further, in thehoneycomb filter, the porous partition wall functions as a filter thattraps the particulate matter in exhaust gas. Hereinafter, theparticulate matter contained in exhaust gas may be referred to as “PM.”The “PM” is an abbreviation of “particulate matter.”

Exhaust gas is purified by a honeycomb filter as described below. First,the honeycomb filter is disposed such that the inflow end face side ispositioned on the upstream side of an exhaust system through whichexhaust gas is emitted. The exhaust gas flows into inflow cells from theinflow end face side of the honeycomb filter. Then, the exhaust gas thathas flowed into the inflow cells passes through a porous partition wall,flows toward outflow cells, and is emitted from the outflow end face ofthe honeycomb filter. When passing through the porous partition wall, PMand the like in the exhaust gas are trapped and removed.

[Patent Document 1] JP-A-2002-219319

[Patent Document 2] International Publication No. 2006/030811

A honeycomb filter used to purify exhaust gas emitted from an automobileengine has been adopting, as a porous partition wall, a high-porosityporous body having high porosity. In recent years, there has been ademand for improvement in the filtration efficiency of honeycomb filtersdue to the tightening of automobile emission regulations and the like.

As a means for improving the filtration efficiency of a honeycombfilter, for example, a method of reducing the average pore diameter of aporous partition wall can be cited. However, the average pore diameterof the partition wall significantly influences the pressure loss of thehoneycomb filter, and there has been a problem that the pressure loss ofthe honeycomb filter inconveniently increases when the average porediameter of the partition wall is reduced.

SUMMARY OF THE INVENTION

The present invention has been made in view of the problems with theprior arts described above. The present invention provides a honeycombfilter which has high trapping performance and reduces pressure loss,and further exhibits high purification performance by being loaded withan exhaust gas purifying catalyst.

According to the present invention, a honeycomb filter described belowis provided.

(1) A honeycomb filter including:

a pillar-shaped honeycomb structure body having a porous partition walldisposed to surround a plurality of cells which serve as fluid throughchannels extending from a first end face to a second end face; and

a plugging portion provided at an open end on the first end face side orthe second end face side of each of the cells,

wherein the partition wall is composed of a material containingcordierite as a main component thereof,

porosity of the partition wall measured by a mercury press-in method is60 to 68%,

an average pore diameter of the partition wall measured by a mercurypress-in method is 13 to 18 μm, and

in a pore diameter distribution which indicates a cumulative pore volumeof the partition wall measured by a mercury press-in method, with a porediameter (μm) on an abscissa axis and a log differential pore volume(cm³/g) on an ordinate axis, a first peak that includes a maximum valueof the log differential pore volume has a pore diameter value of 15 μmor less, the pore diameter value corresponding to a ⅓ value width of amaximum value of the log differential pore volume.

(2) The honeycomb filter described in the foregoing (1), wherein a ratioof the volume of pores that have pore diameters exceeding 20 μm withrespect to a total pore volume of the partition wall is below 40% in thepore diameter distribution.

(3) The honeycomb filter described in the foregoing (2), wherein a ratioof the volume of pores that have pore diameters exceeding 20 μm withrespect to a total pore volume of the partition wall is below 30% in thepore diameter distribution.

(4) The honeycomb filter described in any one of the foregoing (1) to(3), wherein the ratio of the volume of pores that have pore diametersbelow 5 μm with respect to the total pore volume of the partition wallis below 10% in the pore diameter distribution.

(5) The honeycomb filter described in any one of the foregoing (1) to(4), wherein an exhaust gas purifying catalyst is loaded inside thepores of the partition wall.

The honeycomb filter in accordance with the present invention providesan effect of enabling high trapping performance and reduction ofpressure loss. More specifically, the honeycomb filter in accordancewith the present invention has an average pore diameter of the partitionwall thereof set to 13 to 18 μm and the porosity of the partition wallthereof set to 60 to 68%, thereby making it possible to reduce pressureloss while maintaining mechanical strength. In addition, the honeycombfilter in accordance with the present invention is configured such that,in the pore diameter distribution of partition wall, the first peak thatincludes the maximum value of the log differential pore volume has apore diameter value of 15 μm or less, the pore diameter valuecorresponding to the ⅓ value width of the maximum value of the logdifferential pore volume. Consequently, the pore diameter distributionof the partition wall has a sharp first peak, thus making it possible toreduce a large pore volume ratio attributable to pores having relativelylarge pore diameters. Further, the honeycomb filter in accordance withthe present invention has the pore diameter distribution describedabove, and has the average pore diameter of the partition wall set to 13to 18 μm, so that, when the porous partition wall is loaded with anexhaust gas purifying catalyst, the catalyst is loaded such that thecatalyst is uniformly coated inside the pores of the partition wall. Theloading of the catalyst in such a manner enables both improvement oftrapping performance and reduction in pressure loss of the honeycombfilter loaded with the catalyst. Further, the honeycomb filter inaccordance with the present invention can be expected to improvepurification performance because a gas flow becomes uniform after theloading of a low amount of a catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing an embodiment of ahoneycomb filter in accordance with the present invention viewed from aninflow end face side;

FIG. 2 is a plan view of the honeycomb filter shown in FIG. 1 viewedfrom the inflow end face side;

FIG. 3 is a sectional view schematically showing a section A-A′ of FIG.2, and

FIG. 4 is a graph showing the pore diameter distributions of thehoneycomb filters of Examples 1 and 3 and Comparative Example 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe embodiments of the present invention;however, the present invention is not limited to the followingembodiments. Therefore, it should be understood that those created byadding changes, improvements or the like to the following embodiments,as appropriate, on the basis of the common knowledge of one skilled inthe art without departing from the spirit of the present invention arealso covered by the scope of the present invention.

(1) Honeycomb Filter

As shown in FIG. 1 to FIG. 3, a first embodiment of the honeycomb filterin accordance with the present invention is a honeycomb filter 100 thatincludes a honeycomb structure body 4 and plugging portions 5. Thehoneycomb structure body 4 is a pillar-shaped structure having a porouspartition wall 1 disposed so as to surround a plurality of cells 2 thatserve as fluid through channels extending from a first end face 11 to asecond end face 12. In the honeycomb filter 100, the honeycomb structurebody 4 is pillar-shaped and further includes a circumferential wall 3 onthe outer circumferential side face. In other words, the circumferentialwall 3 is provided to encompass the partition wall 1 provided in a gridpattern. The plugging portions 5 are provided at open ends on the firstend face 11 side or the second end face 12 side of each of the cells 2.

FIG. 1 is a perspective view schematically showing an embodiment of thehoneycomb filter in accordance with the present invention viewed from aninflow end face side. FIG. 2 is a plan view of the honeycomb filtershown in FIG. 1, viewed from the inflow end face side. FIG. 3 is asectional view schematically showing a section A-A′ of FIG. 2.

In the honeycomb filter 100, the partition wall 1 constituting thehoneycomb structure body 4 is configured as described below. First, thepartition wall 1 is composed of a material that contains cordierite asthe main component thereof. The partition wall 1 is preferably composedof cordierite except for components that are inevitably contained.

In the honeycomb filter 100, the porosity of the partition wall 1 is 60to 68%. The values of the porosity of the partition wall 1 are obtainedby measurement using a mercury press-in method. The porosity of thepartition wall 1 can be measured using, for example, Autopore 9500(trade name) manufactured by Micromeritics. To measure the porosity, apart of the partition wall 1 is cut out as a test piece from thehoneycomb filter 100, and the test piece obtained in such a manner canbe used for the measurement. For example, the porosity of the partitionwall 1 is preferably 60 to 65% and more preferably 62 to 65%.

Setting the porosity of the partition wall 1 to 60 to 68% enables thepressure loss to be reduced. If the porosity of the partition wall 1 isbelow 60%, the effect of reducing the pressure loss of the honeycombfilter 100 cannot be fully obtained. On the other hand, if the porosityof the partition wall 1 exceeds 68%, then the mechanical strength of thehoneycomb filter 100 inconveniently deteriorates.

In the honeycomb filter 100, the average pore diameter of the partitionwall 1 is 13 to 18 μm. The value of the average pore diameter of thepartition wall 1 is obtained by measurement using the mercury press-inmethod. The average pore diameter of the partition wall 1 can bemeasured using, for example, Autopore 9500 (trade name) manufactured byMicromeritics. The measurement of the average pore diameter can beperformed using the foregoing test piece for measuring the porosity. Theaverage pore diameter of the partition wall 1 is preferably 15 to 18 μm,for example.

Setting the average pore diameter of the partition wall 1 to 13 to 18 μmenables the trapping performance to be improved while reducing thepressure loss. If the average pore diameter of the partition wall 1 isbelow 13 μm, then it is undesirable in that the pressure loss increasesand the purification performance deteriorates, because, when a smallamount of an exhaust gas purifying catalyst is loaded, it becomesdifficult to uniformly coat the catalyst onto the inside of the pores ofthe partition wall 1. On the other hand, if the average pore diameter ofthe partition wall 1 exceeds 18 μm, then the effect of improving thefiltration efficiency of the honeycomb filter 100 cannot be fullyobtained.

Further, the honeycomb filter 100 has a first peak configured asdescribed below in a pore diameter distribution, which shows thecumulative pore volume of the partition wall 1 measured by the mercurypress-in method, with a pore diameter (μm) on the abscissa axis and alog differential pore volume (cm³/g) on the ordinate axis. Here, thefirst peak is a peak that includes a maximum value of the logdifferential pore volume in the pore diameter distribution. Regardingthe first peak, the pore diameter value that corresponds to the ⅓ valuewidth of the maximum value of the log differential pore volume of thefirst peak is 15 μm or less. Here, “the ⅓ value width” means the widthof the first peak at the ⅓ value of the maximum value of the logdifferential pore volume of the first peak. The width of the first peakis determined on the basis of the value of the pore diameter (μm) shownon the abscissa axis. Hereinafter, “the value of a pore diametercorresponding to the ⅓ value width of the maximum value of the logdifferential pore volume of the first peak” may be referred to simply as“the ⅓ value width of the first peak.”

If the ⅓ value width of the first peak is 15 μm or less, then the firstpeak will be sharp in the pore diameter distribution of the partitionwall 1, thus making it possible to reduce a large pore volume ratio dueto pores having relatively large pore diameters and a small pore volumeratio due to pores having relatively small pore diameters. Consequently,both improvement of trapping performance and reduction in pressure lossof the honeycomb filter 100 loaded with an exhaust gas purifyingcatalyst can be achieved. If the ⅓ value width of the first peak exceeds15 μm, then the first peak becomes wide (broad), making it difficult toobtain the two effects described above. There is no particularrestriction on the lower limit value of the ⅓ value width of the firstpeak, but the lower limit value is, for example, 5 μm. Accordingly, the⅓ value width of the first peak is preferably 5 to 15 μm, and morepreferably 10 to 15 μm.

The cumulative pore volume of the partition wall 1 is indicated by avalue measured by the mercury press-in method. The measurement of thecumulative pore volume of the partition wall 1 can be performed using,for example, Autopore 9500 (trade name) manufactured by Micromeritics.The measurement of the cumulative pore volume of the partition wall 1can be performed by the following method. First, a part of the partitionwall 1 is cut out from the honeycomb filter 100 to make a test piece formeasuring the cumulative pore volume. There is no particular restrictionon the size of the test piece, but the test piece is preferably, forexample, a rectangular parallelepiped having a length, a width, and aheight of approximately 10 mm, approximately 10 mm, and approximately 20mm, respectively. There is no particular restriction on a portion of thepartition wall 1 from which the test piece is cut out, but the testpiece is preferably made by cutting out from the vicinity of the centerof the honeycomb structure body in the axial direction. The obtainedtest piece is placed in a measurement cell of a measurement device, andthe interior of the measurement cell is decompressed. Next, mercury isintroduced into the measurement cell. Next, the mercury that has beenintroduced into the measurement cell is pressurized, and the volume ofthe mercury pushed into the pores existing in the test piece is measuredduring the pressurization. At this time, as the pressure applied to themercury is increased, the mercury is pushed into the pores progressivelyfrom pores having larger pore diameters and then to pores having smallerpore diameters. Consequently, the relationship between “the porediameters of the pores formed in the test piece” and “the cumulativepore volume” can be determined from the relationship between “thepressure applied to the mercury” and “the volume of the mercury pushedinto the pores.” The “cumulative pore volume” refers to, for example, avalue obtained by accumulating the pore volumes from a maximum porediameter to a particular pore diameter.

The “pore diameter distribution of the partition wall 1, with the porediameter on the abscissa axis and the log differential pore volume onthe ordinate axis” can be shown by, for example, a graph having the porediameter (unit: μm) indicated on the abscissa axis and the logdifferential pore volume (unit: cm³/g) indicated on the ordinate axis.Such a graph may be, for example, the graph shown in FIG. 4. The graphof FIG. 4 shows the pore diameter distributions of the honeycomb filtersof Examples 1 and 3, and Comparative Example 1 in the examples whichwill be discussed later. In FIG. 4, the honeycomb filters of Examples 1and 3 correspond to the honeycomb filters of the present embodiment. Thehoneycomb filter of Comparative Example 1 is a conventional honeycombfilter to be compared.

The graph showing the pore diameter distributions as shown in FIG. 4will be described in further detail. The graph shown in FIG. 4 is agraph indicating the relationship between “Pore diameter (μm)” and “Logdifferential pore volume (cm³/g).” When the pressure is graduallyapplied to intrude the mercury into the pores of the sample in acontainer hermetically sealed to a vacuum state by the mercury press-inmethod, the mercury under the pressure progressively intrudes intolarger pores and then into smaller pores of the sample. Based on thepressure and the amount of mercury intruded at that time, the porediameters of the pores formed in the sample and the pore volumes can becalculated. Hereinafter, when the pore diameters are denoted by D1, D2,D3 . . . , a relationship of D1>D2>D3 . . . is to be satisfied. Here, anaverage pore diameter D between measurement points (e.g., from D1 to D2)can be indicated on the abscissa axis by “the average pore diameterD=(D1+D2)/2.” Further, the Log differential pore volume on the ordinateaxis can be indicated by a value obtained by dividing an increment dV ofthe pore volume between measurement points by a difference value treatedas the logarithms of the pore diameters (i.e., “log(D1)−log (D2).” In agraph showing such a pore diameter distribution, a peak means a turningpoint indicated by the distribution, and a peak that includes themaximum value of the log differential pore volume is defined as thefirst peak.

In the pore diameter distribution of the partition wall 1, the ratio ofthe volume of pores having pore diameters exceeding 20 μm with respectto the total pore volume of the partition wall 1 is preferably below40%. This configuration makes it possible to reduce a large pore volumeratio attributable to pores having relatively large pore diameters, thusenabling further improvement of the trapping performance. The ratio ofthe volume of pores having pore diameters exceeding 20 μm is furtherpreferably below 30%.

In the pore diameter distribution of the partition wall 1, the ratio ofthe volume of pores having pore diameters below 5 μm with respect to thetotal pore volume of the partition wall 1 is preferably below 10%. Thisconfiguration makes it possible to reduce a small pore volume ratioattributable to pores having relatively small pore diameters, thusenabling a further reduction in pressure loss. The ratio of the volumeof pores having pore diameters below 5 μm is further preferably below7%. The ratio of the volume of pores having pore diameters exceeding 20μm and the ratio of the volume of pores having pore diameters below 5 μmcan be determined from the cumulative pore volume of the partition wall1 or a graph showing pore diameter distributions as shown in FIG. 4.

There is no particular restriction on the thickness of the partitionwall 1, but the thickness of the partition wall 1 is, for example,preferably 0.20 to 0.30 mm, more preferably 0.20 to 0.26 mm, andespecially preferably 0.20 to 0.24 mm. The thickness of the partitionwall 1 can be measured using, for example, a scanning electronmicroscope or a microscope. If the thickness of the partition wall 1 istoo thin, it is undesirable in that the trapping performancedeteriorates. On the other hand, if the thickness of the partition wall1 is too thick, it is undesirable in that the pressure loss increases.

There is no particular restriction on the shapes of the cells 2 formedin the honeycomb structure body 4. For example, the shapes of the cells2 in the section that is orthogonal to the extending direction of thecells 2 may be polygonal, circular, elliptical or the like. A polygonalshape may be triangular, quadrangular, pentagonal, hexagonal, octagonalor the like. The shapes of the cells 2 are preferably triangular,quadrangular, pentagonal, hexagonal or octagonal. Further, regarding theshapes of the cells 2, all the cells 2 may have the same shape ordifferent shapes. For example, although not shown, quadrangular cellsand octagonal cells may be mixed. Further, regarding the sizes of thecells 2, all the cells 2 may have the same size or different sizes. Forexample, although not shown, among the plurality of cells, some cellsmay be made large and the other cells may be made relatively smaller. Inthe present invention, “the cells 2” mean the spaces surrounded by thepartition wall 1.

The cell density of the cells 2 defined by the partition wall 1 ispreferably 30 to 50 cells/cm², and more preferably 35 to 50 cells/cm².This configuration enables the honeycomb filter 100 to be suitably usedas a filter for purifying exhaust gas emitted from an automobile engine.

The circumferential wall 3 of the honeycomb structure body 4 may beconfigured integrally with the partition wall 1 or may be composed of acircumferential coat layer formed by applying a circumferential coatingmaterial to the circumferential side of the partition wall 1. Forexample, although not shown, the circumferential coat layer can beprovided on the circumferential side of the partition wall after thepartition wall and the circumferential wall are integrally formed andthen the formed circumferential wall is removed by a publicly knownmethod, such as grinding, in a manufacturing process.

There is no particular restriction on the shape of the honeycombstructure body 4. The honeycomb structure body 4 may be pillar-shaped,the shapes of the first end face 11 (e.g., the inflow end face) and thesecond end face 12 (e.g., the outflow end face) being circular,elliptical, polygonal or the like.

There is no particular restriction on the size of the honeycombstructure body 4, e.g. the length from the first end face 11 to thesecond end face 12, and the size of the section that is orthogonal tothe extending direction of the cells 2 of the honeycomb structure body4. Each size may be selected as appropriate such that optimumpurification performance is obtained when the honeycomb filter 100 isused as a filter for purifying exhaust gas.

In the honeycomb filter 100, the plugging portions 5 are provided at theopen ends on the first end face 11 side of predetermined cells 2 and atthe open ends on the second end face 12 side of the remaining cells 2.If the first end face 11 is defined as the inflow end face, and thesecond end face 12 is defined as the outflow end face, then the cells 2which have the plugging portions 5 placed at the open ends on theoutflow end face side and which have the inflow end face side open aredefined as inflow cells 2 a. Further, the cells 2 which have theplugging portions 5 placed at the open ends on the inflow end face sideand which have the outflow end face side open are defined as outflowcells 2 b. The inflow cells 2 a and the outflow cells 2 b are preferablyarranged alternately with the partition wall 1 therebetween. This, inaddition, preferably forms a checkerboard pattern by the pluggingportions 5 and “the open ends of the cells 2” on both end faces of thehoneycomb filter 100.

The material of the plugging portions 5 is preferably a material that ispreferred as the material of the partition wall 1. The material of theplugging portions 5 and the material of the partition wall 1 may be thesame or different.

The honeycomb filter 100 preferably has the partition wall 1, whichdefines the plurality of cells 2, loaded with an exhaust gas purifyingcatalyst. Loading the partition wall 1 with a catalyst refers to coatingthe catalyst onto the surface of the partition wall 1 and the innerwalls of the pores formed in the partition wall 1. This configurationmakes it possible to turn CO, NOx, HC or the like in exhaust gas intoharmless substances by catalytic reaction. In addition, the oxidation ofPM of trapped soot or the like can be accelerated. In the honeycombfilter 100 of the present embodiment, the catalyst is particularlypreferably loaded inside the pores of the porous partition wall 1. Thisconfiguration makes it possible to achieve both improvement of thetrapping performance and reduction in the pressure loss after theloading of a low amount of the catalyst. Further, after the catalyst isloaded, a gas flow becomes uniform, so that improvement of purificationperformance can be expected.

There is no particular restriction on the catalyst with which thepartition wall 1 is loaded. For example, such a catalyst can be acatalyst which contains a platinum group element and which contains anoxide of an element of at least one of aluminum, zirconium, and cerium.The loading amount of the catalyst is preferably 50 to 100 g/L, and morepreferably 60 to 90 g/L. In the present specification, the loadingamount of a catalyst (g/L) indicates the amount (g) of a catalyst loadedper unit volume (L) of the honeycomb filter.

(2) Manufacturing Method of the Honeycomb Filter

There is no particular restriction on the manufacturing method of thehoneycomb filter of the present embodiment shown in FIG. 1 to FIG. 3,and the honeycomb filter can be manufactured by the method describedbelow. First, a plastic kneaded material for manufacturing a honeycombstructure body is prepared. The kneaded material for manufacturing thehoneycomb structure body can be prepared, for example, as describedbelow. Talc, kaolin, alumina, aluminum hydroxide, silica, and the likeare used as raw material powders, and these raw material powders can beblended to obtain a chemical composition that contains silica in therange of 42 to 56% by mass, alumina in the range of 30 to 45% by mass,and magnesia in the range of 12 to 16% by mass.

Next, the kneaded material obtained as described above is subjected toextrusion so as to manufacture a honeycomb formed body having apartition wall that defines a plurality of cells, and an outer wallprovided to encompass the partition wall.

The obtained honeycomb formed body is dried by, for example, microwaveand hot air, and the open ends of the cells are plugged using the samematerial as the material used for manufacturing the honeycomb formedbody, thereby making plugging portions. The honeycomb formed body may befurther dried after making the plugging portions.

Next, the honeycomb formed body with the plugging portions added theretois fired to manufacture a honeycomb filter. The firing temperature andthe firing atmosphere differ according to the raw materials. A personskilled in the art can select a firing temperature and a firingatmosphere best suited to the selected materials.

EXAMPLES

The following will describe in more detail the present invention byexamples, but the present invention is not at all limited by theexamples.

Example 1

For the cordierite forming raw material, talc, kaolin, alumina, aluminumhydroxide, and porous silica were prepared. Then, the cumulativeparticle size distribution of each raw material was measured using alaser diffraction/scattering type particle diameter distributionmeasurement device (trade name: LA-960) manufactured by HORIBA, Ltd. InExample 1, the raw materials were blended to prepare the cordieriteforming raw materials such that the blending ratios (parts by mass) ofthe raw materials exhibited the values shown in Table 1. In Table 1, thehorizontal row of “Particle size D50 (μm)” shows the particle diameterof 50% by volume (i.e., a median diameter) of each raw material.

Next, 3.0 parts by mass of a water absorbable polymer as an organic poreformer, 6.0 parts by mass of a binder, 1 part by mass of a surfactant,and 77 parts by mass of water were added to 100 parts by mass of acordierite forming raw material to prepare a kneaded material. As thewater absorbable polymer, a water absorbable polymer, the particlediameter of 50% by volume of which was 30 μm, was used. As the binder,methylcellulose was used. As a dispersing agent, a potassium lauratesoap was used. Table 2 shows the blending ratios (parts by mass) of theorganic pore formers and other raw materials. In Table 2, the horizontalrow of “Particle size D50 (μm)” shows the particle diameter of 50% byvolume (i.e., the median diameter) of the organic pore formers. Further,the blending ratios (parts by mass) shown in Table 2 indicate the ratioswith respect to 100 parts by mass of the cordierite forming rawmaterial.

Next, the obtained kneaded material was extruded by an extruder tomanufacture a honeycomb formed body. Subsequently, the obtainedhoneycomb formed body was dried by high frequency dielectric heating,and then further dried using a hot air dryer. The shape of the cells inthe honeycomb formed body was quadrangular.

Next, the plugging portions were formed in the dried honeycomb formedbody. First, the inflow end face of the honeycomb formed body wasmasked. Then, the end portion provided with the mask (the end portion onthe inflow end face side) was immersed in plugging slurry, and the openends of the cells without the mask (the outflow cells) were filled withthe plugging slurry. Thus, the plugging portions were formed on theinflow end face side of the honeycomb formed body. Then, the sameprocess was repeated on the outflow end face of the dried honeycombformed body thereby to form the plugging portions also in the inflowcells.

Next, the honeycomb formed body in which the plugging portions had beenformed was dried with a microwave dryer, and further dried completelywith a hot air dryer, and then both end faces of the honeycomb formedbody were cut and adjusted to a predetermined size. Subsequently, thedried honeycomb formed body was degreased and fired to manufacture thehoneycomb filter of Example 1.

The honeycomb filter of Example 1 had an end face diameter of 118 mm anda length of 127 mm in the extending direction of the cells. Further, thethickness of the partition wall was 0.20 mm, and the cell density was 47cells/cm². The values of the partition wall thickness and the celldensity are shown in Table 3.

On the honeycomb filter of Example 1, the porosity and the average porediameter of the partition wall were measured by the following method.The results are shown in Table 3. In addition, the cumulative porevolume of the partition wall was also measured, and based on themeasurement result, the total pore volume of the pores formed in thepartition wall was determined. Further, each of the ratios of the volumeof pores below 5 μm, the volume of pores of 5 to 20 μm, and the volumeof pores exceeding 20 μm with respect to the foregoing total pore volumewas calculated. The results are shown in Table 3. Further, based on thecumulative pore volume of the partition wall, a pore diameterdistribution indicating the pore diameter (μm) on the abscissa axis andthe log differential pore volume (cm³/g) on the ordinate axis wascreated, and the ⅓ value width (μm) of the first peak of the porediameter distribution was determined. The results are shown in Table 3.

TABLE 1 Blending ratio of cordierite forming raw material (parts bymass) Talc Kaolin Alumina Aluminum hydroxide Fused silica Porous silicaParticle size D50 10 20 5 6  1  3 25 20 (μm) Example 1 40 — 19 14 — 15 —12 Example 2 40 — 19 14 — 15 — 12 Example 3 40 — 19 14 — 15 — 12Comparative Example 1 — 40 16 10 22 — 12 — Comparative Example 2 — 40 1914 — 15 — 12

TABLE 2 Blending ratio of organic pore former Blending ratio of otherraw materials (parts by mass) (parts by mass) Material Foamable resinWater absorbable polymer Binder Surfactant Water Particle size D50 45  25   30 — — — (μm) Example 1 — — 3.0 6.0 1 77 Example 2 — — 3.0 6.0 1 78Example 3 — — 4.0 6.0 1 86 Comparative Example 1 9.0 0.5 — 6.0 1 26Comparative Example 2 — — 3.0 6.0 1 77

TABLE 3 Partition ⅓ value wall Average width of Pore volume ratio (%)with respect to thickness Cell density Porosity pore dia. 1st peak totalpore volume (mm) (cells/cm²) (%) (μm) (μm) Below 5 μm 5~20 μm Over 20 μmExample 1 0.20 47 63 15 15 6.5 69.5 24.0 Example 2 0.23 39 63 16 12 3.074.9 22.1 Example 3 0.24 47 65 18 14 1.9 60.9 37.2 Comparative Example 10.30 36 65 21 21 1.3 44.0 54.7 Comparative Example 2 0.25 47 65 19 182.3 50.9 46.8

(Porosity)

The measurement of the porosity of the partition wall was performedusing Autopore 9500 (trade name) manufactured by Micromeritics. In themeasurement of the porosity, a part of the partition wall was cut outfrom the honeycomb filter to obtain a test piece, and the porosity wasmeasured using the obtained test piece. The test piece was a rectangularparallelepiped having a length, a width, and a height of approximately10 mm, approximately 10 mm, and approximately 20 mm, respectively. Thesampling location of the test piece was set in the vicinity of thecenter of the honeycomb structure body in the axial direction.

(Average Pore Diameter)

The measurement of the average pore diameter of the partition wall wasperformed using Autopore 9500 (trade name) manufactured byMicromeritics. The test piece used for measuring the porosity was usedalso for measuring the average pore diameter. The average pore diameterof the partition wall is indicated by a value calculated by defining theaverage pore diameter as a pore diameter providing a volume that is halfa total pore volume by the mercury press-in method.

(Cumulative Pore Volume)

The measurement of the cumulative pore volume of the partition wall wasperformed using Autopore 9500 (trade name) manufactured byMicromeritics. The test piece used for measuring the porosity was usedalso for measuring the cumulative pore volume.

On the honeycomb filter of Example 1, the filtration efficiency, thepressure loss, and the purification performance were evaluated by thefollowing method. The results are shown in Table 4. The evaluation ofeach of the filtration efficiency, the pressure loss, and thepurification performance was performed according to the following methodby loading each honeycomb filter to be evaluated with a catalystcontaining a platinum group element.

(Catalyst Loading Method)

First, a catalyst slurry containing aluminum oxide having an averageparticle diameter of 30 μm was prepared. Then, using the preparedcatalyst slurry, the honeycomb filter was loaded with the catalyst. Tobe specific, the loading of the catalyst was performed by dipping thehoneycomb filter, then excess catalyst slurry was blown away by air soas to load the partition wall of the honeycomb filter with apredetermined amount of the catalyst. Thereafter, the honeycomb filterloaded with the catalyst was dried at a temperature of 100° C. and wasfurther subjected to heat treatment at 500° C. for two hours so as toobtain a honeycomb filter with the catalyst. The loading amount ofcatalyst with which the honeycomb filter of Example 1 was loaded was 90g/L.

(Filtration Efficiency)

First, exhaust gas purification devices were fabricated by using thehoneycomb filters with catalysts of the examples and the comparativeexamples as the exhaust gas purifying filters. Then, each of thefabricated exhaust gas purification devices was connected to an outletside of an engine exhaust manifold of a 1.2 L direct injection typegasoline engine vehicle, and the number of soot particles contained inthe gas emitted from the outlet port of the exhaust gas purificationdevice was measured by a PN measurement method. As for the driving mode,a driving mode (RTS95) that simulates the worst of RDE driving wasimplemented. The total number of soot particles emitted after thedriving in the mode was taken as the number of soot particles of theexhaust gas purification device to be determined, and the filtrationefficiency (%) was calculated from the number of soot particles. Thecolumn of “Filtration efficiency ratio” of Table 4 shows the values ofthe filtration efficiency (%) of the exhaust gas purification deviceusing the honeycomb filter with the catalyst of each of the examples andthe comparative examples when the value of the filtration efficiency ofthe exhaust gas purification device using the honeycomb filter with thecatalyst of Comparative Example 1 is defined as 100%. In the evaluationof the filtration efficiency, the honeycomb filter of each of theexamples and the comparative examples was evaluated according to thefollowing evaluation standard.

Evaluation “Excellent”: If the value of the filtration efficiency ratio(%) exceeds 110%, then the evaluation is determined as “Excellent.”

Evaluation “Good”: If the value of the filtration efficiency ratio (%)is greater than 105% and equal to or less than 110%, then the evaluationis determined as “Good.”

Evaluation “Acceptable”: If the value of the filtration efficiency ratio(%) is greater than 100% and equal to or less than 105%, then theevaluation is determined as “Acceptable.”

Evaluation “Fail”: If the value of the filtration efficiency ratio (%)is equal to or less than 100%, then the evaluation is determined as“Fail.”

(Pressure Loss)

The exhaust gas emitted from a 1.2 L direct injection type gasolineengine was introduced at a flow rate of 600 m³/h at 700° C., and thepressures on the inflow end face side and the outflow end face side ofeach of the honeycomb filters with the catalysts were measured. Then,the pressure loss (kPa) of each of the honeycomb filters with thecatalysts was determined by calculating the pressure difference betweenthe inflow end face side and the outflow end face side. The column of“Pressure loss ratio” of Table 4 shows the value (%) of the pressureloss of the honeycomb filter with the catalyst of each of the examplesand the comparative examples when the value of the pressure loss of thehoneycomb filter with the catalyst of Comparative Example 1 is definedas 100%. In the evaluation of the pressure loss, the honeycomb filter ofeach example was evaluated according to the following evaluationstandard.

Evaluation “Excellent”: If the value of the pressure loss ratio (%) isequal to or less than 90%, then the evaluation is determined as“Excellent.”

Evaluation “Good”: If the value of the pressure loss ratio (%) isgreater than 90% and equal to or less than 95%, then the evaluation isdetermined as “Good.”

Evaluation “Acceptable”: If the value of the pressure loss ratio (%) isgreater than 95% and equal to or less than 100%, then the evaluation isdetermined as “Acceptable.”

Evaluation “Fail”: If the value of the pressure loss ratio (%) exceeds100%, then the evaluation is determined as “Fail.”

(Purification Performance)

First, exhaust gas purification devices that use the honeycomb filterswith the catalysts of the examples and the comparative examples as theexhaust gas purifying filters were fabricated. Each of the fabricatedexhaust gas purification devices was connected to an outlet side of anengine exhaust manifold of a 1.2 L direct injection type gasoline enginevehicle, and the concentration of NOx contained in the gas emittedthrough the outflow port of the exhaust gas purification device wasmeasured to determine the NOx purification ratio. The column of“Purification performance ratio” of Table 4 shows the value of the NOxpurification ratio (%) of each of the exhaust gas purification devicesusing the honeycomb filters with the catalysts of the examples and thecomparative examples when the value of the NOx purification ratio of theexhaust gas purification device using the honeycomb filter with thecatalyst of Comparative Example 1 is defined as 100%. In the evaluationof the purification performance, the honeycomb filter of each exampleand each comparative example was evaluated according to the followingevaluation standard.

Evaluation “Excellent”: If the value of the purification performanceratio (%) is equal to or greater than 105%, then the evaluation isdetermined as “Excellent.”

Evaluation “Good”: If the value of the purification performance ratio(%) is greater than 102% and below 105%, then the evaluation isdetermined as “Good.”

Evaluation “Acceptable”: If the value of the purification performanceratio (%) is greater than 100% and equal to or less than 102%, then theevaluation is determined as “Acceptable.”

TABLE 4 Evaluation of filtration Evaluation of pressure Evaluation ofpurification efficiency loss performance Filtration Pressure lossPurification Evaluation efficiency ratio Evaluation ratio Evaluationperformance ratio Example 1 Excellent 112% Good 92% Acceptable 102%Example 2 Excellent 117% Excellent 84% Good 104% Example 3 Good 110%Acceptable 98% Excellent 105% Comparative Example 1 Reference 100%Reference 100%  Reference 100% Comparative Example 2 Acceptable 103%Fail 103%  Good 103%

Examples 2 and 3

In Examples 2 and 3, the blending ratios (parts by mass) of the rawmaterials used for the cordierite forming raw material were changed asshown in Table 1. In addition, the blending ratios (parts by mass) ofthe organic pore formers and other raw materials were also changed asshown in Table 2. Except that these raw materials were used to preparethe kneaded material, the honeycomb filters were manufactured by thesame method as that of Example 1.

Comparative Examples 1 and 2

In Comparative Examples 1 and 2, the blending ratios (parts by mass) ofthe raw materials used for the cordierite forming raw material werechanged as shown in Table 1. In addition, the blending ratios (parts bymass) of the organic pore formers and other raw materials were alsochanged as shown in Table 2. Except that these raw materials were usedto prepare the kneaded material, the honeycomb filters were manufacturedby the same method as that of Example 1. In Comparative Example 1, afoamable resin having a particle size D50 of 45 μm was used as a poreformer in addition to the water absorbable polymer as an organic poreformer. In Table 2, the column of “Organic pore former” shows theblending ratios (parts by mass) of the foamable resin as a pore former.

The porosity and the average pore diameter of the partition wall of eachof the honeycomb filters of Examples 2 and 3 and Comparative Examples 1and 2 were also measured by the same method as that of Example 1.Further, the cumulative pore volume of the partition wall was alsomeasured, and based on the measurement result, the total pore volume ofthe pores formed in the partition wall was determined, and then theratio of each of the volume of pores below 5 μm, the volume of pores of5 to 20 μm, and the volume of pores exceeding 20 μm with respect to thetotal pore volume was calculated. In addition, based on the cumulativepore volume of the partition wall, a pore diameter distributionindicating the pore diameter (μm) on the abscissa axis and the logdifferential pore volume (cm³/g) on the ordinate axis was created, andthe ⅓ value width (μm) of the first peak of the pore diameterdistribution was determined. The results are shown in Table 3. Among thegraphs indicating the pore diameter distributions created as describedabove, the graphs indicating the pore diameter distributions of thehoneycomb filters of Examples 1 and 3 and Comparative Example 1 areshown in FIG. 4.

The honeycomb filters of Examples 2, 3 and Comparative Examples 1, 2were loaded with the catalysts by the same method as that of Example 1.On each of the honeycomb filters loaded with the catalysts (honeycombfilters with the catalysts), the filtration efficiency, the pressureloss, and the purification performance were evaluated by the same methodas that of Example 1. The results are shown in Table 4.

RESULTS

It was verified that the honeycomb filters of Examples 1 to 3 aresuperior to the honeycomb filter of Comparative Example 1, whichprovides the reference, in all evaluations of filtration efficiency,pressure loss, and purification performance. Consequently, it was foundthat the honeycomb filters of Examples 1 to 3 have excellent trappingperformance, can suppress an increase in pressure loss, and furtherexhibit excellent purification performance, in comparison with theconventional honeycomb filter. On the other hand, the evaluation resultsof the honeycomb filter of Comparative Example 2 were inferior to thoseof the honeycomb filters of Examples 1 to 3 in terms of the filtrationefficiency, the pressure loss, and the purification performance, thedeterioration of the pressure loss in particular being marked.

INDUSTRIAL APPLICABILITY

The honeycomb filter in accordance with the present invention can beused as a trapping filter for removing particulates and the likecontained in exhaust gas.

DESCRIPTION OF REFERENCE NUMERALS

1: partition wall; 2: cell; 2 a: inflow cell; 2 b: outflow cell; 3:circumferential wall; 4: honeycomb structure body; 5: plugging portion;11: first end face; 12: second end face; and 100: honeycomb filter.

What is claimed is:
 1. A honeycomb filter comprising: a pillar-shapedhoneycomb structure body having a porous partition wall disposed tosurround a plurality of cells which serve as fluid through channelsextending from a first end face to a second end face; and a pluggingportion provided at an open end on the first end face side or the secondend face side of each of the cells, wherein the partition wall iscomposed of a material containing cordierite as a main componentthereof, porosity of the partition wall measured by a mercury press-inmethod is 60 to 68%, an average pore diameter of the partition wallmeasured by a mercury press-in method is 13 to 18 μm, and in a porediameter distribution which indicates a cumulative pore volume of thepartition wall measured by a mercury press-in method, with a porediameter (μm) on an abscissa axis and a log differential pore volume(cm³/g) on an ordinate axis, a first peak that includes a maximum valueof the log differential pore volume has a pore diameter value of 15 μmor less, the pore diameter value corresponding to a ⅓ value width of amaximum value of the log differential pore volume.
 2. The honeycombfilter according to claim 1, wherein a ratio of the volume of pores thathave pore diameters exceeding 20 μm with respect to a total pore volumeof the partition wall is below 40% in the pore diameter distribution. 3.The honeycomb filter according to claim 2, wherein a ratio of the volumeof pores that have pore diameters exceeding 20 μm with respect to thetotal pore volume of the partition wall is below 30% in the porediameter distribution.
 4. The honeycomb filter according to claim 1,wherein a ratio of the volume of pores that have pore diameters below 5μm with respect to a total pore volume of the partition wall is below10% in the pore diameter distribution.
 5. The honeycomb filter accordingto claim 1, wherein an exhaust gas purifying catalyst is loaded insidethe pores of the partition wall.